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LED Signal LL-136

Railway LED light source

LL-136 is an LED light source intended for use in railway colour light signals. It was developed as a replacement for two-filament light bulbs in legacy, relay-based interlocking systems, as well as a light source for signals in modern, electronic-based interlocking systems.

Light source of LL-136 consists of seven individually controlled and monitored LEDs and has four possible operation states:
1. Normal operation
2. Cold thread test
3. Single LED failure
4. Signal failure
Normal operation
LL-136 enters normal operation if the correct input voltage is applied and all seven LEDs are operational. In normal operation state, signal has three operational modes:
1. Day-time operation
2. Night-time operation
3. Blinking operation
In day-time operation, LEDs are driven by 100% PWM signal, and LL-136 draws maximum input power. In night-time operation, LEDs are driven by 60% PWM signal and input power is 60% of that in day-time operation. Blinking operation is carried out by alternately switching the signal off and driving the signal by the day/night-time voltage at a nominal frequency of 1 Hz with 50% duty cycle.
Cold thread test
Cold thread test is an optional feature that allows an interlocking to check the availability of the signal. In the cold thread test, LEDs are not lighted, but the microcontroller is active and the signal draws current indicating that that all LEDs are operational. If one or more LEDs fail, LL-136 doesn’t draw current in the cold thread test state.
Single LED failure
When single LED failure is detected, the Advanced warning signal (AWS) is generated and the LL-136 remains operational. The Advanced warning output is implemented as a potential-free, normally closed relay contact.
Signal failure
When two or more LEDs fail, signal enters failure mode and will not light nor draw input current of more than 0.1 ARMS regardless of the input voltage.




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